1. Field of the Invention
The present invention relates to a mount board for mounting electronic components thereon, and to a semiconductor module including the mount board.
2. Description of the Related Art
In recent years, high density and low thermal resistance have been demanded for mount boards that are used for mounting electronic components including semiconductor chips such as large scale integration (LSI) chips thereon. High density is demanded because the pin counts of LSI chips have increased and the use of multichip modules that include a plurality of semiconductor chips has become widespread. Low thermal resistance is demanded because the power consumption of LSI chips has increased and because of factors related to end products.
In general, a mount board for a multichip module has to have a set of electrode terminals for each of the semiconductor chips in the multichip module. Thus, wiring on a side on which the semiconductor chips are mounted has been multi-layered. Therefore, a multilayer wiring board called a build-up board is used as a mount board (see, for example, Japanese Patent No. 2739726). In general, a build-up substrate includes a core board and wiring layers laminated symmetrically on the upper and lower surfaces of the core board.
A semiconductor chip, such as an LSI chip, or a semiconductor package including a semiconductor chip sealed therein are mounted on a mount board such that the semiconductor chip or the semiconductor package is electrically and mechanically connected to the uppermost wiring layer through, for example, bumps. Japanese Unexamined Patent Application Publication No. 07-176873 discloses a technique in which a semiconductor chip is fixed to a bonding pad using a die bonding member and electrically connected to the uppermost wiring layer by wire bonding. In addition, Japanese Unexamined Patent Application Publication No. 07-176873 discloses a technique in which heat generated by a semiconductor chip is radiated to the atmosphere through the uppermost wiring layer of build-up layers.
When semiconductor devices such as semiconductor chips and semiconductor packages are mounted on the uppermost layer of build-up wiring layers, a part of heat generated by the semiconductor chips and the semiconductor packages is transferred through the uppermost layer to inner wiring layers (under layers) connected to the uppermost layer.